#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;

const int N = 510, M = 10010;

struct Edge {
	int a, b, c;
}edges[M];

int n, m, k;
int dist[N];
int last[N];

void bellman_ford() {
	memset(dist, 0x3f, sizeof dist);
	dist[1] = 0;
	
	for (int i = 0; i < k; i ++ ) {
		memcpy(last, dist, sizeof dist);
		for (int j = 0; j < m; j ++ ) {
			auto e = edges[j];
			dist[e.b] = min(dist[e.b], last[e.a] + e.c);
		}
	}
}

int main() {
	scanf("%d%d%d", &n, &m, &k);
	
	for (int i = 0; i < m; i ++ ) {
		int a, b, c;
		scanf("%d%d%d", &a, &b, &c);
		edges[i] = {a, b, c};
	}
	
	bellman_ford();
	
	if (dist[n] > 0x3f3f3f3f / 2) puts("impossible");
	else printf("%d\n", dist[n]);
	
	return 0; 
} 